The invention discloses an intra mode prediction method, an intra mode prediction device and a coder. The method comprises the following steps of: when the optimal mode of an adjacent left block is a horizontal mode, taking the horizontal mode as the most possible mode of a block to be coded; when the optimal mode of an adjacent upper block is a vertical mode, taking the vertical mode as the most possible mode of the block to be coded; when the optimal modes of the adjacent left block and the adjacent upper block are the same, taking the same mode as the most possible mode of the block to be coded; when the serial numbers of the optimal modes of the adjacent left block and the adjacent upper block belong to a set {8, 6}, taking the horizontal mode as the most possible mode of the block to be coded, and when the mode serial numbers of the optimal modes of the adjacent left block and the adjacent upper block belong to a set {3, 4} or {7, 5}, taking the vertical mode as the most possible mode of the block to be coded; and selecting the optimal mode in the optimal modes of the adjacent left block and the adjacent upper block, which has a smaller mode serial number, as the most possible mode of the block to be coded. The embodiment of the invention can improve the accuracy of intra mode prediction.